In an electronic switching system, digital data is generally multiplexed by using a time division multiplexing scheme. For example, an E1-type link of 2.048 Mbps includes 32 time slots, each time slot corresponding to a data channel. In order to monitor a particular channel, it is necessary to extract data transferred through the channel among the multiple channels.
Referring to FIG. 1, there is provided a block diagram of a conventional data monitoring apparatus 100 which comprises a keyboard 110, a CPU (central processing unit) 120, a channel signal generator 130, a rate converter 140 and a protocol processor 150. The data monitoring apparatus 100 is connected to a digital link L141 which transfers time division multiplexed data, e.g., an E1-type 2.048 Mbps link having 32 channels.
The multiplexed data is applied to the rate converter 140 of the data monitoring apparatus 100. At the rate converter 140, data transferred from a selected one of the 32 channels is extracted and its transmission rate is converted to a predetermined rate, e.g., 64 Kbps, at which the data is processed at the data analyzer 150. And the rate-converted data is applied to the data analyzer 150 which monitors the data. At the data analyzer 150, the applied data is analyzed to check whether or not data is transferred properly through the selected channel.
In the conventional monitoring apparatus, in order to select the channel to monitor, a channel information is applied to the CPU 120 via the keyboard 110 by using a channel input program, e.g., a pull-down menu program as well known. The CPU 120 outputs the channel information signal and a write-enable signal through the line L121 and L122 respectively to the channel signal generator 130. When receiving the channel information signal and the write-enable signal, the channel signal generator 130 applies a channel selection signal to the rate converter 140.
For example, numeral 5 is inputted at the keyboard by using the channel selection menu of the input program when the 5th channel of the 32 channels is to be monitored. Channel information of the numeral 5 is transferred to the CPU 120 where it is analyzed to generate a 5-bit channel information signal `00101` and to make the write-enable signal active. When the write-enable signal becomes active, the channel signal generator 130 receives the channel information signal from the CPU 120. The channel signal generator 130 generates a channel selection signal which retains high-state during the interval corresponding to the selected channel and low-state during the intervals corresponding to the remaining channels or vice versa. The rate converter 140 converts the transmission rate of the channel indicated by the channel selection signal to the 64 Kbps.
However, since the monitored channel should be selected by using the keyboard at the menu program, the channel monitoring procedure includes a complicated and time-consuming channel selection procedure. And, there is no element for displaying the selected channel visually in the conventional data monitoring apparatus.